Electronic devices, such as portable electronic devices, are often able to be powered by an external power supply that supplies power to operate electronic circuits and also to recharge internal batteries. Some portable electronic devices receive power through external data communications interfaces, such as Universal Serial Bus (USB) interfaces. The USB standard defines a required electrical current capacity that a USB interface must be able to supply to connected devices. Devices that receive power pack charging power through a standard USB interface are also able to be connected to power supplies, such as modular wall mounted power supplies with a USB connector, that are capable of delivering electrical current in excess of the capacity specified by the USB specification.
However, electrical current through a USB port is limited to the level specified by the USB standard unless power supply capacity is able to be determined and a no reliable maximum electrical current can be assumed to be provided through non-USB power interfaces.